Defence Minister Harjit Sajjan has signalled the Liberal government is prepared to debate the orthodoxy of the western military alliance's non-binding spending targets at the upcoming NATO leaders summit in Brussels next week.

In 2014, NATO introduced a 10-year program that asks its 29 members to spend the equivalent of two per cent of their gross domestic product on defence.

Though the majority of those nations aren't currently meeting the target, Lute says no one expected it to be an overnight turnaround and the overall situation is what he'd describe as "glass half-full."

Canada has long been singled out for lagging when it comes to meeting that target. Sajjan says it's partly because the federal government is too bashful when it comes to what it describes as defence spending.

"We've been too Canadian in how we calculate our two per cent compared to other nations," Sajjan told CBC News earlier this month.

National Defence Minister Harjit Sajjan tells Power & Politics that NATO burden sharing is about more than just investments. 3:44

"We're always too modest. When I looked at the calculation, I looked at how some nations add certain things that we haven't."

The Liberals' most recent defence policy plans to increase the defence budget to $32 billion per year by 2026-27. That boost still only brings Canada's defence spending to 1.4 per cent of GDP.

Trump has been especially critical of nations not meeting that two per cent target.

"The United States is increasingly unwilling to ignore this alliance's failure to meet shared security challenges," reads a letter he sent to Justin Trudeau.

The NATO summit will be the first time the prime minister and the president have met since the G7 summit in June, which culminated in Trump removing the U.S. from the final communique and tweeting insults at Trudeau from Air Force One on the way to meet North Korean leader Kim Jong-un.

Navigating that relationship will be a particular challenge at the NATO meeting, because Trump hasn't made his intentions for the future of the alliance clear, Lute said.